Method and apparatus for accurate calibration of VUV reflectometer

Abstract

A calibration technique is provided that utilizes a standard sample that allows for calibration in the wavelengths of interest even when the standard sample may exhibit significant reflectance variations at those wavelengths for subtle variations in the properties of the standard sample. A second sample, a reference sample may have a relatively featureless reflectance spectrum over the same spectral region and is used in combination with the calibration sample to achieve the calibration. In one embodiment the spectral region may include the VUV spectral region.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to Provisional Patent Application No. 60 / 600,599 filed Aug. 11, 2004; the disclosure of which is expressly incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]The present invention relates to the field of optical metrology. More specifically, it provides a method by which broad-band vacuum ultraviolet (VUV) reflectance data may be accurately calibrated. Additionally, it also provides a method by which highly accurate thin film measurements may be performed.[0003]Optical reflectometry techniques have long been employed in process control applications in the semiconductor manufacturing industry due to their non-contact, non-destructive and generally high-throughput nature. The vast majority of these tools operate in some portion of the spectral region spanning the deep ultraviolet and near-infrared wavelengths (DUV-NIR generally 200-1000 nm). The push towards thinner layers and the introduction...

AI Technical Summary

Benefits of technology

[0016]One embodiment of the current invention provides a means by which VUV reflectance data may be quickly and accurately calibrated. In one embodiment, the method enables simultaneous calibration of reflectance data covering a broad range of wavelengths. Additionally, the technique operates in a manner well suited for use in semiconductor manufacturing environments.

[0017]The method may be self-contained in that it may not require use of a second referencing instrument. It may provide a method by which calibration results may be autonomously verified such that use of third party certified standards will be reduced and / or altogether eliminated.

[0021]In another embodiment of the current invention a technique by which highly accurate thin film measurements may be performed is provided. The method may provide mathematical fitting algorithms with a more sensitive “goodness of fit” indicator that is less susceptible to noise present in the raw data. The fitting routine may be a spectrally driven fitting routine rather than relying solely on an amplitude driven routine (which typically incorporates difference calculations). In such an embodiment, the measurements may be obtained by utilizing the presence of sharp, narrow spectral features.

Problems solved by technology

The push towards thinner layers and the introduction of complicated new materials have challenged the sensitivity of such instrumentation.

While such methods offer a means of obtaining calibrated reflectance data, they generally suffer from the fact that they are time-consuming, involve considerable mechanical motion and can not easily be integrated into systems suitable for use in semiconductor manufacturing environments.

Integration of a separate reference ellipsometer into an optical measurement system in order to calibrate the first optical measurement device is both complicated and expensive.

Additionally, it would be advantageous if this method specifically enabled the accurate calibration of reflectometry data at wavelengths encompassing the VUV spectral region, where small uncertainties in the properties of third party certified standards can result in substantial errors.

Unfortunately, there are limits to the measurement accuracy that can be attained using conventional “goodness of fit” parameters.

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